1. Technical Field
This invention relates to a combined cycle power plant, and more particularly to a combined cycle power plant that utilizes a biomass gasifier that supplies fuel to an internal combustion engine.
2. Background of the Invention
A combined cycle power plant is described in a paper entitled xe2x80x9cDiesel Combined Cycles Using Fired Boilersxe2x80x9d, by T. P. Davis, and F. M. Shelor presented at the Power-Gen Americas conference in Orlando, Fla. on Dec. 7-9, 1994. Such power plant includes a prime-mover diesel engine generator combined with a boiler having specially designed burners supplied with the diesel exhaust for producing steam, and a Rankine cycle steam turbine. Both the diesel and the burners are supplied with natural gas or light distillate oil. And, since up to 20% of the total fuel input heat to a diesel is rejected to engine coolant, this low level heat (less than 200xc2x0 F.) is available to preheat feed water in the steam cycle.
When only low quality fuels such as biomass fuels, e.g., sawdust, are available, however, the only practical utilization of such fuels is by way of gasification. In such case, it has been suggested to generate power by fueling diesel generators with the combustible gas produced by the gasifier utilizing the diesel exhaust as a heat source for an unfired heat recovery steam generator. Because of the high efficiency of present diesels, however, exhaust temperatures are relatively low. As a result, energy recovery from the exhaust is low, and the steam quality produced is less than ideal for energy production.
It is therefore an object of the present invention to provide a new and improved combined cycle power plant operating with biomass fuels which has performance characteristics superior to those known in the prior art.
A combined cycle power plant according to the present invention includes a gasifier for converting biomass material, or low grade coal, etc., to combustible gases and producing heat, and an internal combustion engine coupled to a generator for burning the combustible gases and driving the generator which produces power. The internal combustion engine rejects heat and produces hot exhaust gases. A vaporizer, which is a part of a power cycle turbine unit, containing a working fluid, preferably, an organic fluid is responsive to the hot exhaust gases for vaporizing the organic fluid and producing vaporized organic fluid which is supplied to an organic vapor turbine preferably coupled to a generator. The turbine expands the vaporized organic fluid driving the generator thus producing power and expanded vaporized organic fluid which is condensed in a condenser. The condensate produced by the condenser is returned to the vaporizer. At least some of the heat produced by the gasifier is transferred to the organic fluid in the vaporizer. Preferably, at least some of the heat rejected by the internal combustion engine is transferred the organic fluid in a preheater interposed between the condenser and the vaporizer.
An embodiment of the invention is described by way of example, and with reference to the accompanying drawing.